1. Field of the Invention
This invention relates to a method for the production of a catalyst for purifying exhaust gases, which removes harmful components contained in an exhaust gas from the internal combustion engine such as an automobile by utilizing a container-integrated carrier. Specifically, it relates to a method for the production of a catalyst for purifying exhaust gases, which simultaneously removes harmful components such as carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxides (NOx) contained in an exhaust gas from the internal combustion engine such as an automobile by utilizing the container-integrated carrier.
2. Description of Related Art
Various kinds of exhaust gas purifying catalysts have been proposed for removing harmful components in the exhaust gas, which emanates from the internal combustion engine.
various studies regarding the improvement of engines have been pursued for the purpose of coping with the global reinforcement of the exhaust gas control in recent years. There are effective methods for decreasing the wall thickness of a honeycomb carrier for reducing the thermal capacity or increasing the cell density thereof for improving the geometric surface area with a view of elevating the temperature of a catalyst bed immediately after start of the engine and accelerating the ignition speed of the catalyst. Thus, the use of the carrier of such a quality results in improvement in the purifying property of the catalyst. However, it brings about problems that the carrier or catalyst is degraded in strength because of a decrease in the wall thickness of the carrier, so that the carrier or catalyst is sustained chipping or fracture during transportation of the carrier or during the application of a catalytically active component to the carrier or canning of the catalyst into a converter.
It is disclosed in JP-A-02-264,110, JP-A-08-42,333, and JP-A-11-76,837 that the fracture of the carrier such as the edge chipping mentioned above can be decreased by inserting a catalyst into a metallic cylinder and then immobilizing the inserted catalyst with a mat. These official gazettes, however, include no mention of a method for depositing a catalytically active component to the carrier. It entails disadvantages that the catalyst slurry adheres to part of the container in the case of deposition of the active component to such a container-integrated carrier, that there is out of order in welding the container to the exhaust pipe of a vehicle, that the carrier retainer is degraded in retaining force, and that the catalyst performance is declined.
This invention, in producing an exhaust gas purifying catalyst by using a ceramic carrier of a thin wall thickness with a view of coping with the reinforcement of the exhaust gas control in recent years, is to provide a method for producing a high-performance exhaust gas purifying catalyst without inflicting damage such as edge chipping on the carrier or without suffering from a catalyst slurry defiling the welded portions of the container, the retainer, and so on.
We have pursued a diligent study to solve the problem in search of a method which comprises obtaining a container-integrated type carrier by inserting a honeycomb carrier into a metallic cylinder in advance of the production of a catalyst and then immobilizing the inserted carrier with a retainer such as a mat, and causing a catalytically active component to deposit on the carrier. We have consequently developed method for producing a catalyst without inflicting damage such as edge chipping on a carrier and without defiling the welded portions of the container or the retaining mat with the active component even if a ceramic carrier with a small wall thickness is used.
Specifically, an object of this invention is accomplished by a method for the production of an exhaust gas purifying catalyst which is characterized by using a container-integrated type carrier having a ceramic carrier retained in a metallic cylinder through a retaining mat, inserting a sealing jig between the metallic cylinder and the carrier, forcing it to the retaining mat, and thereafter depositing a catalytically active component on the carrier.
In accordance with the present method, the catalyst is produced without inflicting damage such as edge chipping upon the carrier that excels in productivity and allows the cost of production to decrease.
In accordance with the present method, the active component is deposited substantially only on the carrier, so that it can be easily managed.
The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments.